1. Field Of The Invention
The present invention relates to a powertrain component for use in an internal combustion engine. More particularly, the invention relates to a component having a hard, wear resistant film having a graded composition formed thereupon.
2. Related Art Statement
In most internal combustion engines, there are various powertrain components. Whether or not the powertrain component operates in an oil-starved environment, traditional problems of noise, vibration, and wear have resulted from frictional and normal forces generated between adjacent interacting surfaces, particularly over prolonged periods at high operating temperatures.
Illustrative of approaches to such problems is EP 435 312 Al which was published on Jul. 3, 1991. That reference discloses a hard and lubricous thin film of amorphous carbon-hydrogen-silicon and a process for producing the film by heating in a vacuum at 600.degree. C. The disclosed film is applied to an iron-base metallic material, thereby forming a hard coating of low friction. However, at such temperatures, there may be a tendency to melt the substrate, and if the substrate is made of steel, to detemper it. Additionally, there may be a loss of net shape.
Formation of hard, lubricous films (also referred to as "coatings") on substrates can be accomplished by several known processes. Such processes include radio frequency (RF), ion beam and microwave plasma chemical vapor deposition (CVD) and physical vapor deposition (PVD) techniques. If applied satisfactorily, such coatings could reduce friction and wear. Depending on the technique used, several problems may remain. They include delamination of the film in an operating environment, which may be occasioned in part by compressive stresses engendered during deposition at the film/substrate interface. In general, the thicker the film, the higher the compressive stresses engendered during film formation. If such stresses are excessive, delamination may result. Other problems may arise from chemical incompatibility of the substrate and the coating.
As an example, aluminum and its alloys have been among those substrates with which conventional deposition techniques have yielded only marginal results. This is because, in part, aluminum carbides tend to be water soluble and unstable, especially in conditions of prolonged exposure to high humidity. Accordingly, the direct application of carbonaceous films to an aluminum-containing substrate may be intrinsically problematic.
Against this background, the need has arisen to devise a powertrain component and method for preparing a substrate-coating system which has a reliably adherent hard, wear resistant film, while accommodating compressive stresses generated during film formation and avoiding problems associated with chemical incompatibility between the film and the substrate.
The need has also arisen for a substrate-interlayer-film system which permits surface engineering of a wide variety of substrate materials to enhance friction, wear, and chemical characteristics. Ideally, such a system would permit simultaneous optimization of adhesion to the substrate, mechanical properties, stress state of the interlayer, friction, and wear properties of the resulting surface.